Ticks are hematophagous arthropods that feed on a wide diversity of hosts. Unlike this group of arthropods, the Ixodid adult female ticks have the characteristics to ingest blood for an extended period of over 2 weeks.
Completion of the blood meal is dependent on the relationships of ticks with hosts species. Resistance to tick infestation implicates both innate and acquired immunity, and is characterized by reduced feeding, molting and mating capabilities that may lead to the death of the parasite. Acquired immunity of resistant hosts is mediated by a polarized Th1-type immune response, involving IFN-γ production and delayed type hypersensitivity reaction.
Some hosts are unable to counteract the tick infestation. Indeed, during their blood meal, ticks circumvent host defences via pharmacologically active components secreted in their saliva. These factors can modulate both the innate and the acquired immunity of the host. In this way, the leukocyte responsiveness is modified during tick feeding. For example, cytokines production is modulated, inducing a polarised Th2 immune response.
Therefore, the complex tick-host molecular interaction can be considered as a balance between host defences raised against the parasite and the tick evasion strategies, facilitating feeding for an extended period. Although, there is extensive information about the effects of tick bioactive factors on host immune defences, little is known about the mechanisms of their actions. However, it has been observed that a wide range of new proteins is expressed during the blood meal. Several of them might be essential for the completion of the tick feeding process.